1. FIELD OF THE INVENTION
The present invention relates generally to the orthotic field and, more particularly, to orthotic knee braces used by patients suffering a deficiency of the knee function due to injuries of the ligaments or connective tissues.
2. PRIOR ART & GENERAL BACKGROUND
Several knee braces intended to provide a stabilizing function to an injured knee are described in the prior art. Such braces usually provide rigid mechanical-limiting stops to prevent the knee from hyperextension or to provide some elastic force to counter the knee's extension forces. A more recent approach includes a pneumatic enclosure of the knee that creates a large amount of mechincal opposition to both flexion or extension, which, however, causes severe limitation of movement and therefore is not wholly desireable.
For typical prior art approaches, see U.S. Pat. No. 4,397,308 involving the so-called Dynasplint System, U.S. Pat. No. 4,407,276 and U.S. Pat. No. Des. 269,379. Note also Lew, William D., M.S., et al., Orthotics and Prosthetics, "A Comparison of Pistoning Forces in Orthotic Knee Joint," Vol. 36, No. 2, Summer 1982, pp. 85-95; Lewis, Jack L., Ph.D., et al., Orthotics and Prosthetics, "A New Concept in Orthotics Joint Design--The Northwestern University Knee Orthosis System," Vol. 37, No. 4, Winter 1983-84, pp. 15-23; and Lewis, Jack L., Ph.D., et al., Orthotics and Prosthetics, "A New Concept in Orthotics Joint Design--The Northwestern University Knee Orthosis System Part II: The Complete Orthosis," Vol. 38, No. 1, Spring 1984, pp. 13-28. Further, see U.S. Pats. Nos. 4,337,764 ("ZINCO"); and 4,280,489. See also U.S. Pat. Nos. 3,955,565 and 4,361,142.
Such prior art devices, if they provide any interaction at all to prevent knee joint dislocation, typically severaly limit the range of motion of the leg of the patient, and thus are undesireable.
Since most of the ligaments, cartilage or connective tissue of the knee which is injured and/or subsequently removed provides a natural retaining action to the knee's bones during knee and leg movement and flexion or extension, it is necessary and desireable to provide such retaining action in an orthotic knee brace, without severely limiting the natural range of movement of the knee and leg. This has not been provided by any known prior art knee brace. It is also necessary to require the terminal angular velocity during extension or flexion to that which will not induce displacement of the joint bones relative to each other when the leg is fully extended or flexed.
A substantial difference between the retaining action generated by the system of the present invention compared to that of the devices of the prior art which severely limit the range of motion is the prevention of the terminal impact, which is present in prior art devices. Such terminal impact is transfered to the tissue, causing excessive pressure, discomfort and skin laceration. The present invention, by virtue of not limiting the range of motion, also allows the user to maintain normal movement patterns of the knee and leg without imposing on the wearer the necessity of having to modify his or her walking pattern as do prior art devices. Those prior art devices cause the wearer to work in a disadvantageous manner and substantially increase the demands upon the legs muscles, causing premature fatigue and general increase in metabolic energy expenditure.
An important advantage of providing the retaining force to the knee, a with the present device, while undergoing the necessary extremes of range of motion is that such retaining force satisfies the equilibrium of the joint, substituting for the lost retaining force of the injured ligament as described by P. Renstrom, et al. American Journal of Sports Medicine, Vol. 14, No. 1, pages 83-87, 1986, in particular as shown in FIGS. 3, 4, 5 and 6 of that publication.
Such equilibrium could be described by the equation as follows in the case of extension EQU F.sub.Q =F.sub.L +F.sub.EL
or, quadriceps muscle force=ligament force+external load.
When the ligament is injured or removed, equilibrium is disturbed, causing the displacement of the bones, which can be prevented if the ligament retaining force is substituted for by the leverage mechanism retaining force described in the present invention.